How Marijuana Suppresses The Immune System

Smoking marijuana can suppress the body's
immune system, which explains why pot-smokers are more susceptible than
non-smokers to certain cancers and infections, according to a new
study.

This effect of marijuana
is due to chemicals in the drug that fire up the body's production of
immune system cells called myeloid-derived suppressor cells. While most
immune system cells are protective — fighting infections and cancers to
keep a person healthy — these cells suppress the immune system, keeping
it in check, according to the study.

"Cannabis is one of the most widely used drugs of abuse
worldwide, and it is already believed to suppress immune functions,
making the user more susceptible to infections and some types of
cancer," Prakash Nagarkatti, a microbiology and pathology professor at
the University of South Carolina, said in a statement.

Nagarkatti and his colleagues focused their study on cannabinoids,
compounds found in the cannabis plant, to see how they affected immune
suppression and tumor growth. Their study included the pain-relieving compound delta-9 tetrahydrocannabinol (THC).

The researchers injected one group of mice with THC and compared them with a group not injected with the compound.

The mice injected with THC had more of the immune-suppressing cells
than the mice who didn't receive THC, according to the study.

The researchers found that marijuana triggered the production of a
massive number of myeloid-derived suppressor cells — leading to immune
suppression and cancer growth — by activating cells that respond to the
cannabinoids found in marijuana, researchers said.

Cancer patients have more of these cells than healthy people. The suppressor cells can even hinder cancer therapy and promote cancer growth, the study said.

"Marijuana cannabinoids present us with a double edged sword,"
Nagarkatti said, because they can cause increased susceptibility to
cancer and infections, but they can also open the door to opportunities
to treat disorders where a suppressed immune system is beneficial, such
as arthritis, multiple sclerosis, lupus and hepatitis.

The study is published in the December issue of the European Journal of Immunology.

Live Science Staff

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